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Assessing the suitability of the Bad River as a reference system for the St Louis River AOC using geochemistry, biotic condition of macroinvertebrates and bioaccumulation of mercury.
Citation:
Lazorchak, Jim, J. Hoffman, M. Mills, K. Fritz, Greg Peterson, M. Pearson, T. Angradi, D. Walters, M. Elliott, S. Janssen, J. DeWild, D. Krabbenhoft, AND E. Pilgrim. Assessing the suitability of the Bad River as a reference system for the St Louis River AOC using geochemistry, biotic condition of macroinvertebrates and bioaccumulation of mercury. 2018 SETAC NA Annual Meeting, Sacramento, California, November 04 - 08, 2018.
Impact/Purpose:
This presentation will cover a large collaborative project conducted under SHC 2.61 and 3.61 where ORD Duluth and Cincinnati, plus states of Minnesota and Wisconsin and USGS conducted a survey of the St Louis AOC to determine the baseline conditions of mercury, biogeochemistry and biotic condition and compared it to a potential reference river, the Bad river. The results of this effort will be presented.
Description:
The St. Louis River Area of Concern (AOC) was designated in 1987 due to Beneficial Use Impairments (BUIs), including “Restrictions on Fish and Wildlife Consumption” (BUI 1) from historical pollutants. Minnesota and Wisconsin posted fish consumption advisories for the St. Louis River, in part, because fish have elevated mercury concentrations. Mercury bioaccumulation in the food web can be from legacy sources in sediment, as well as present-day ambient sources, such as atmospheric deposition. In 2017 a study was conducted to achieve four goals to support the understanding of Hg sources in the AOC : 1) Compare mercury methylation and bioaccumulation by characterizing the macroinvertebrate assemblages, geochemistry, ecosystem type, and food web structure between the AOC and the reference location (Bad River); 2) Compare age- and size-specific mercury residues in select fish species between the AOC and Lower Bad River; 3) Trace food web pathways and identify mercury sources in select fish species using stable isotopes of carbon and nitrogen, and of mercury, respectively; 4) Develop a mercury-specific BUI restoration target for the AOC based on the long-term, post-remediation projected change in fish mercury residues based on the inferred differences in mercury-source bioaccumulation between the AOC and Lower Bad River. For this presentation, we will focus on Goals 1 and 3. For each location, up to five samples each were collected for mayfly (hexagenia) larvae, odonate larvae, riparian spiders, and a composite benthic invertebrate assemblage samples using multi-plate artificial substrate samplers. For Biotic condition and mercury tissue concentrations in macroinvertebrates, a new multi-plate artificial substrate device was employed. Thirty-nine total sites were sampled with 25 sites in the AOC and 14 sites on the Lower Bad River. Sixteen samplers were deployed at each site and left to colonize for 4 weeks. When the samplers were retrieved, 12 of 14 were dissembled, scraped, sieved then picked for biomass. Two samplers were set aside for identification and metabarcoding to assess similarity in benthic communities. Macroinvertebrate assemblage, water, sediment and biota mercury, plus other water quality analyses will be presented and discussed.
